A proportional-integral-derivative (PID) controller is a control loop feedback device commonly used in industrial control systems. A PID controller periodically calculates an error value as the difference between a measured process variable and an intended setpoint. The PID controller attempts to minimize the error over time by adjustment of a control variable, such as the position of a robotic arm supporting a payload.
While PID controllers are applicable to many control problems, PID controllers often perform poorly because PID control is inherently a feedback system using constant parameters, yet with no direct knowledge of the process. Thus overall performance is reactive and a compromise. In one example, when used alone, PID controllers may give poor performance when the PID loop gains are to be reduced so the control system does not overshoot, oscillate, or hunt near the control setpoint value.
Feedforward control is one technique used to improve the shortcomings of conventional (feedback) PID controllers, as feed-forward control incorporates knowledge regarding the system. The PID controller communicates with one actuator responsible for error correction and dynamic torque (feed forward) control. In this configuration, the dynamic (feed forward) torque can be orders of magnitude larger than the torque necessary for corrections on position error. Therefore, a same actuator tasked with providing error correction and dynamic torque control is generally larger, creating space and packaging issues. Furthermore, these actuators need to be replaced or serviced more often, and are not as easily monitored for identification of wear.